N-Glycosylation influences transport, but not cellular trafficking, of a neuronal amino acid transporter SNAT1.

SNAT1 is a system N/A neutral amino acid transporter that primarily expresses in neurons and mediates the transport of l-glutamine (Gln). Gln is an important amino acid involved in multiple cellular functions and also is a precursor for neurotransmitters, glutamate and GABA. In the present study, we demonstrated that SNAT1 is an N-glycoprotein expressed in neurons. We identified three glycosylation sites at asparagine residues 251, 257 and 310 in SNAT1 protein, and that the first two are the primary sites. The biotinylation and confocal immunofluorescence analysis showed that the glycosylation-impaired mutants and deglycosylated SNAT1 were equally capable of expressing on the cell surface. However, l-Gln and 3H-labeled methyl amino isobutyrate (MeAIB) was significantly compromised in N-glycosylation-impaired mutants and deglycosylated SNAT1 when compared with the wild-type control. Taken together, these results suggest that SNAT1 is an N-glycosylated protein with three de novo glycosylation sites and N-glycosylation of SNAT1 may play an important role in the transport of substrates across the cell membrane.